Whether due to degeneration, injury or otherwise, hip and shoulder joints often require replacement. Artificial implants are common in such applications. Such implants, in the hip joint context, often comprise an acetabular prosthesis and a femoral prosthesis. The acetabular prosthesis may comprise an acetabular insert or cup and a dual mobility liner.
The acetabular component typically includes a metal shell which is attached to the pelvic bone and an insert which fits inside the metal shell. A fixed bearing comprises a single mobile articulation between the femoral head and acetabular insert. The insert of a fixed bearing is typically made of an ultra-high-molecular-weight polyethylene (polymer), metal, or ceramic material into which the femoral head typically made of metal or ceramic fits into and articulates. A dual mobility component typically includes a metal insert or similar hard material into which a mobile polymer bearing liner fits into and articulates, and a metal or ceramic femoral head which fits inside and articulates with the mobile bearing liner. Movement can occur between the femoral head and inner surface of the mobile bearing liner and also between the outer surface of the mobile bearing liner and inner surface of the acetabular insert in a dual mobility bearing component. A femoral head of the femoral prosthesis is free to tilt, rotate and swivel within the dual mobility liner which is, in turn, free to tilt, rotate and swivel within the acetabular insert. That is, the dual mobility liner can be tilted, rotated and swiveled between the femoral head and the acetabular insert without affecting the position of the hip joint.
In a fixed bearing constrained acetabular component, which is intended to prevent the femoral head from separating or dislocating from the acetabular component, the liner typically extends beyond a hemisphere to contain the femoral head. In a fixed bearing constrained component with a polymer insert, the insert can expand or deform during insertion of the femoral head to allow the femoral head into the center of the insert. In a constrained acetabular insert of a dual mobility bearing in which the liner is made of a hard metal or similar material, (i.e., an acetabular insert that extends beyond hemisphere to constrain the dual mobility liner contained therein from dislocating), inserting the dual mobility liner (which also extends beyond hemisphere to constrain the femoral head contained therein from dislocating) presents challenges. The present disclosure addresses this need.